The exams watchdog is reporting a rapid increase in the number of pupils being given extra time in exam rooms amid fears that teachers are exploiting rules designed to give dyslexic pupils a fair chance.

The number of pupils appealing to have allowances made because of a personal crisis or illness at the time of their exams also went up last year, prompting suggestions that some could be playing the system to get extra marks.

The Qualifications and Curriculum Authority (QCA) today publishes its annual assessment of last year's exams and in-depth research into attitudes to the exam system, which reveals that there is still strong support for A-levels, despite many teachers questioning the results their pupils got. Some 38% reported a decline in accuracy in the past two years.

The number of pupils given extra time increased to nearly 70,000 last year - a 22% rise on the previous summer, the report says. Schools can award up to 25% extra time at their own discretion for students with particular needs such as dyslexia, while exam boards have to approve longer extensions.

After the exams last summer more than 308,000 requests were made to exam boards to make "special considerations" - with reasons including illness and bereavement.

Ken Boston, the head of the QCA, called for vigilance in schools to ensure the rules were not being exploited.

Some 4,258 students were penalised after being caught cheating - a slight decrease on last year. A third of those were people who had brought study notes, calculators or mobile phones into exam rooms when they were banned.

Some 1,300 students were also penalised for plagiarism. The QCA is considering introducing software to monitor all papers for plagiarism. It would pick up on phrases which had been repeated by students, using the technology designed to identify unusual patterns in credit card expenditure to tackle fraud.

A poll of the attitudes of pupils, teachers, parents and the public towards the exam system, conducted by Ipsos Mori, reveals support for the current system of exams.

A-levels are still an important qualification in the opinion of 93% of teachers. Similarly, only 8% of students believe they should be scrapped.

However, doubts among teachers about the accuracy of A-level marking are revealed. Some 41% do not have confidence in the marking system and 38% believe that quality has declined due to a lack of experienced markers.

More than eight out of 10 teachers said that the annual debate in the media about the "dumbing down" of A-levels was damaging for students, 28% of whom reported being upset by it.

Only a third of students have heard of the new diplomas to be phased in from September, and 57% of teachers reported knowing a fair deal or a lot about the new qualifications.

Steve Sinnott, general secretary of the National Union of Teachers, said: "Of concern is the low level of awareness of the new diploma in its introduction year, particularly among teachers in independent schools. There is still an enormous amount to do to ensure that the diploma is known about and respected by schools, and the general public."

Ken Boston said: "It is encouraging to see that confidence in A-levels and GCSEs continues to grow and that the levels of service provided by awarding bodies to centres satisfies the standards we have set. However, there are still issues that call for vigilance. The number of candidates with access arrangements has increased significantly this year.

"This may be due to an increasingly professionalised body of exam officers who work hard to ensure that candidates get the access they are entitled to, but we need to monitor the situation closely to ensure that the system remains fair for all learners."